Waste Water Engineering Interview Questions and Answers on “Pumps & Pumping Stations – 2”.
1. Pumping stations are necessary where pressures have to be decreased.
a) True
b) False
Answer: b
Clarification: Pumping stations are necessary where water is pumped directly into system o where pressure has to be increased because there is an insufficient difference in water levels in gravity flow distribution systems.
2. The most expensive part is the energy supply for pumps.
a) True
b) False
Answer: a
Clarification: Pumping stations are situated where water has to be pumped into a distribution system or where pressure levels are to be increased. This requires high energy supplies and is expensive.
3. To reduce the expenses, the pumps must have a high degree of ________
a) Flow rate
b) Efficiency
c) Power
d) Intake
Answer: b
Clarification: To reduce the expenses, the pumps must have a high degree of efficiency and must be maintained properly. To guarantee safe water quality, cross connection of drinking water and waste removal systems must be avoided.
4. What are the facilities including pumps and other equipment for pumping fluids from one place to another called?
a) Pumping facilities
b) Pumping stations
c) Pumping house
d) Pump and equipment facilities
Answer: b
Clarification: Pumping stations are used for a variety of infrastructures such as the supply of water to canals, the drainage of low-lying land and the removal of sewage to processing sites.
5. What is a building where the pumps are located and operated called?
a) Pumping station
b) Pump house
c) Pumping facility
d) Pumping house
Answer: b
Clarification: A building where the pumps are located and operated is called a pump house. This consists of pumps of an irrigation system with a pressurized water filtration system.
6. In duplex pump stations, the pumps shall be of __________
a) Same pressure
b) Same efficiency
c) Same capacity
d) Different capacity
Answer: c
Clarification: In duplex pump stations, the pumps shall be of the same capacity. If pumps are in series it is required to meet the capacity of total dynamic head requirement, each set of pumps in series shall be viewed as a single pumping unit.
7. The road way to the pumping station must be a _______
a) Hard surface
b) Muddy road
c) Hilly road
d) Smoother path
Answer: a
Clarification: The road way to the pumping station must be an all-weather roadway. The road way must be provided on a hard surface. Muddy roads lead to inconvenience during the rainy season.
8. In a desalination plant in order to provide high pressure greater than the osmotic pressure which type of pump is selected?
a) Reciprocating Pump
b) Positive Displacement Pump
c) Booster Pump
d) Multistage Pump
Answer: d
Clarification: Multistage Pumps have two/more impellers and a corresponding number of volute cases. Since there are multiple volute cases the pressure obtained is more than that obtained by a single stage pump. However, the volume of the fluid handled remains constant in both the cases.
9. Generally, what is the Material of Construction of the casing of the pumps which are used in a desalination plant?
a) Cast Iron
b) Bronze
c) Stainless Steel SS 304 GRADE
d) Stainless Steel SS 316 L Grade
Answer: d
Clarification: The inlet water of any desalination plant would have a minimum TDS of 25,000 ppm. Since this water has high concentration of ions it can easily corrode the inner parts of the pump. Hence the quality of Steel of 316 L is preferred.
10. Which type of pump is used when chemicals are to be dosed in water treatment plant?
a) Plunger Pump
b) Positive Displacement Pump
c) Vertical Turbine Pump
d) Jet Pump
Answer: b
Clarification: Positive Displacement Pump is used to pump liquids with high viscosity. These are also known as a reciprocating pump. These pumps are used when the fluid to be pumped is at low flow and high pressure.
11. Which is the part of the pump which prevents the flow of water from the volume to enter back to the impeller?
a) Shaft
b) Bearing
c) Mechanical seal
d) Wear rings
Answer: d
Clarification: Water from the high pressure zone of the volute could re-enter the impeller. In order to prevent this a physical separation between the high and low pressure side is provided. Wear ring provides a flow restriction in order to prevent the water from entering the impeller again.
12. For a mechanical seal which is the normal leakage rate?
a) 30-50 drops of seal water/min
b) 40-60 drops of seal water/min
c) 20-40 drops of seal water/min
d) 20-60 drops of seal water/min
Answer: d
Clarification: A normal leakage rate is 20-60 drops of seal water/min. If it is below 20 drops of seal water/min then the operator should gradually loosen the packing gland nuts. He should observe the leakage rate after loosening the gland.
13. In order to reduce the operation and maintenance which of the following characteristics of a pump should be considered?
a) Efficiency of the pump
b) Flow rate
c) NPSH
d) Head
Answer: a
Clarification: Higher the efficiency of the pump lesser will be the power consumed. Hence the electricity consumed by the pump would be low. This will result in a lesser maintenance cost of the pump.
14. Which type of impeller is usually preferred when handling liquids with solids?
a) Closed impeller
b) Open impeller
c) Single suction impeller
d) Double suction impeller
Answer: b
Clarification: Open impellers are used to handle water with a large concentration of solid. Also open impellers get damaged more than the closed impellers as the vanes are exposed directly. These impellers usually handle water which is at a low pressure.
15. Which type of pump is used when the effluent should be pumped back into the plant for use as service water?
a) Vortex Pump
b) Vertical Turbine Pump
c) Sump pump
d) Rotary pump
Answer: b
Clarification: The construction of the turbine pumps enables to handle clean water. Line shaft turbine pump has been used t0 draw water from deep wells. In case the effluent has to be pumped back as service water then Vertical Turbine pumps are apt for the same application.
16. Which formula is used to calculate the head for centrifugal pumps?
a) H=P(PSIG)X144/Specific gravity
b) H=P(PSIG)X2.31/Specific gravity
c) H=P(ft)X144/Specific gravity
d) H=P(ft)X2.31/Specific gravity
Answer: b
Clarification: As pressure increases head too increases. Similarly sp. Gravity is inversely proportional. This formula holds good when the head is measured at psig.
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